The present invention relates to an endoscope image sensing method and apparatus which are suitable for every observation region and realize color reproduction independent of the type of light source.
In general, for endoscope image sensing apparatuses for sensing an object by using an image sensing device such as a CCD (Charge Coupled Device), and obtaining a video signal by photoelectrically converting the sensed image data, it is important to ensure good color reproduction by eliminating variations resulting from different types of light sources and the like. To realize such good color reproduction, various types of adjustments such as white balance adjustment and black balance adjustment are performed.
For example, Jpn. Pat. Appln. KOKAI Publication No. 10-211166 discloses a technique associated with an endoscope image sensing apparatus which realizes good color reproduction by performing white balance and black balance adjustments. This apparatus is further characterized by preventing erroneous use of the white balance and black balance adjustments.
In an endoscope image sensing apparatus using an image sensing device such as a CCD as described above, the luminance and color difference signals obtained by the image sensing device are arithmetically processed by using a uniquely defined matrix (to be referred to as a color matrix hereinafter) consisting of predetermined coefficients, thereby converting the signals into R, G, and B digital signals. The image represented by the signals is then displayed on the screen of a monitor or the like.
Endoscope image sensing apparatuses generally use various types of light sources. For example, FIGS. 8 to 10 respectively show the spectral characteristics of a xenon lamp, halogen lamp, and metal halide lamp. More specifically, FIG. 8 shows the spectral characteristics of a xenon lamp, which are similar to those of natural light and substantially uniform throughout the ultraviolet, visible, and infrared regions. FIG. 9 shows the spectral characteristics of a halogen lamp, which exhibit high output levels across the visible and infrared regions. FIG. 10 shows the spectral characteristics of a metal halide lamp, which exhibit high output levels in the visible region.
In endoscopic diagnoses, different color reproduction are desired depending on the observation regions. For this reason, as in the prior art, it is difficult to realize desired color reproduction by using only a uniquely defined color matrix regardless of the observation region or light source to be used.
If, for example, a one-chip CCD is used, a signal obtained by combining an output from the CCD having spectral sensibility characteristics like those shown in FIG. 11, an output from an infrared cut filter having spectral characteristics like those shown in FIG. 12, and an output form a light source having spectral characteristics like those shown in one of FIGS. 8 to 10 is input to an Y/C separation circuit. If arithmetic operation is performed by using the uniquely defined color matrix described above after the signal is subjected to Y/C separation processing, the operation result varies depending on the light source used. As a consequence, the color reproduction yields different results.
For example, FIG. 13 shows the characteristics obtained by matrix operation using a xenon lamp as a light source. FIG. 14 shows the characteristics obtained by matrix operation using a halogen lamp as a light source. Obviously from the two graphs, the color reproduction result in one operation differ from that in the other operation.